Again, there's not a single word that does what you want. Since this is for non-native English speakers, you may as well use the simplest, most direct choice of words. If you're really looking for a single word, you could try jihad or movement, but these have all kinds of other connotations and don't work well for your stated purpose

Endeavor, undertaking, task. . . If these words are too big, then stick with "good/great work". It doesn't need to be "catchy" or "impressive" to be effective. Sometimes a clear, simple, direct message is all you need, especially for people who may not know much English.

If you really need some buzzword or catchphrase to make an impact, consider hiring a PR firm!

I'm not sure how "jihad" would come across to your intended audience, but to most people "jihad" means "religion-inspired war". Regardless of what the term really means to Moslems, that's the connotation. If you're trying to change that perception, I'd consider whether an appeal for a non-violent and/or non-Islamic charity is the best place to do that.
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JayAug 24 '12 at 19:41

@Jay Agreed, I just had to throw it out there. Additionally, in emails I get for "calls to action" (i.e. donate) I see wording like this: "The struggle for reproductive rights is ongoing. Your involvement is needed on many issues. Get active and make your voice heard by joining..." The word choice definitely gives off a political vibe, but it suits its purpose since politics are involved here. I think how to frame a "good deed" is really determined by your audience.
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ZairjaAug 24 '12 at 19:50

We tend to play greatness down in the UK - it may be a national failing, but results in descriptors such as great endeavour or noble work sounding rather pompous or naive. Jihad and crusade can sound very threatening. We'd probably stick with (very) worthwhile project.

I don't know your audience, but in general, I'd be cautious about trying too hard to sound profound and important. If you try to sound profound and don't get it quite right, you often end up sounding pretentious or just plain silly.